Tobacco smoking is a leading cause of preventable death and disability in the U.S. Although women compared to men are at a greater risk of smoking-related disease morbidity and mortality, research suggests they may smoke for different reasons than men and have a harder time quitting than men. Research identifying female-specific factors underlying addiction is critical for: (a) addressing sex-related health disparities; (b) informing female-specific treatments; and (c) discovering addiction processes that are overrepresented among females yet applicable to both sexes. Ovarian hormones represent a female specific factor implicate in the maintenance of nicotine addiction and success following a quit attempt. This proposal aims to advance this line of research by combining ecological momentary assessment (EMA) with daily hormonal sampling across an entire menstrual cycle to further examine the patterns and mechanisms of ovarian hormone variation effects on smoking in women in real time. The use of prospective daily recordings and hormonal sampling will allow us to test whether smoking will be higher on days with high estrogen and lower on days with high progesterone (Aim 1), that women with greater estrogen to progesterone ratios compared to women with lower estrogen to progesterone ratios across the entire menstrual cycle will smoke more and be more nicotine dependent (Aim 2), and that days with higher estrogen will be marked by greater nicotine reward and worse cognitive control, which will mediate relations between higher estrogen and increased smoking (Aim 3). Secondary aims will explore variability of hormonal effects across the menstrual cycle (Aim 4). As the first comprehensive study investigating daily changes in ovarian hormones, drug reward, cognitive control, and smoking behavior, this project will pave the way for a program of research involving more intensive laboratory and field-based studies of psychoneuroendocrinological underpinnings of smoking in women. Through expert mentoring, directed readings, formal coursework and seminars, onsite training, attending national scientific meetings, manuscript and grant preparation, mentorship of students in the USC Health, Emotion, and Addiction Laboratory, and the completion of the proposed investigation expertise will be gained in: (a) Naturalistic field assessment of nicotine addiction; (b) EMA design and implementation; and (c) Use of advanced statistical methodology to test the aims outlined by the project. Thus, by the end of the proposed training period, the applicant will be uniquely positioned to run an independent interdisciplinary line of research incorporating both lab and field based studies in investigating female specific factors in addiction.